This invention is generally directed to toner compositions, and their use thereof in electrophotographic imaging systems. More specifically, the present invention is directed to the incorporation of colored polymeric dyes in toner and developer compositions where leaching or bleeding of the colorant is substantially eliminated. Without leaching there are enabled toner compositions that retain their color fidelity or intensity over extended time periods. Also, the dyed toner and developer compositions of the present invention are useful in various electrophotographic imaging systems, particularly colored imaging systems having incorporated therein as the photoconductive member a layered imaging device which is negatively or positively charged.
Toner and developer compositions including colored developer compositions are well known. These compositions usually contain toner particles consisting of a resin and colorants, and carrier particles. With regard to colored developer compositions, the colorants are usually selected from cyan dyes or pigments, magenta dyes or pigments, yellow dyes or pigments, and mixtures thereof. There are thus disclosed in U.S. Pat. No. 3,844,815 colored developer compositions containing as the yellow pigment Foron Yellow, while U.S. Pat. No. 4,035,310 discloses colored toner compositions comprised of pigment Yellow 97, and carrier particles generally comprised of steel coated with various polymeric resinous substances.
Also, it is known that one of the main advantages of selecting organic dyes instead of pigments for color toner compositions resides in the provisions of increased color fidelity as the dyes can be molecularly dispersed in the toner resins. To obtain a homogeneous dispersion, however, it is generally necessary to build into these molecules certain substituents for enhancing their compatibility with the toner resin. Unless the dye molecules are substantially fully compatible with the toner resins, they have a tendancy to aggregate with time, especially when subjected to heat, pressure and humidity thereby resulting in a loss of color fidelity. Additionally, the low molecular weight of the dye molecules causes a high lability or mobility of the dye molecules in the toner resin resulting in undesirable bleeding of the dyes.
Several prior art patents also disclose the incorporation into toner compositions, as separate components, charge enhancing additives, which additives may in an amount of from 0.1 to about 10 percent by weight be added to the compositions of the present invention, primarily for the purpose of imparting a positive charge to the toner resin particles. There is thus disclosed in U.S. Pat. No. 4,298,672, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions containing resin particles and pigment particles, and as a charge enhancing additive alkyl pyridinium compounds and their hydrates of the formula as detailed in column 3, beginning at line 14. Examples of alkyl pyridinium compounds disclosed include cetyl pyridinium chloride. Moreover, there is disclosed in U.S. Pat. No. 4,338,390, the disclosure of which is totally incorporated herein by reference, positively charged toner compositions having incorporated therein as charge enhancing additives various organic sulfate and sulfonate compositions, including stearyl dimethyl phenylethyl ammonium paratoluene sulfonate. Further, in U.S. Pat. No. 3,893,935 there is described the use of quaternary ammonium salts as charge control agents for electrostatic toner compositions.
Additionally, there are disclosed in the prior art colored toner and developer compositions containing as charge enhancing additives para-halophenylcarboxylic acids, and the salts thereof. More specifically, there are disclosed in the prior art negatively charged toner compositions containing resin particles; dye particles such as cyan, magenta, or yellow dyes; and as a charge enhancing additive in an amount of from about 0.1 percent by weight to about 10 percent by weight parahalophenylcarboxylic acids, and the salts thereof, including 4-fluorobenzoic acid, 4-chlorobenzoic acid, and 4-bromobenzoic acid. The aforementioned additives may also be incorporated into the toner compositions of the present invention.
Other prior art includes U.S. Pat. No. 3,699,135, which discloses polymeric dyes prepared by the copolymerization of a specific silane with a derivative of an anthraquinone containing two aliphatic hydroxy groups; and U.S. Pat. Nos. 3,232,691; 3,549,304 and 4,101,269. These references disclose that the functional group formed on the chromophore enters into the polymerization reaction with the monomer leaving the chromophore as a pendant moiety in the polymer structure. Of background interest, there were selected as representative prior art U.S. Pat. Nos. 3,027,362; 3,117,957; 3,337,288; 3,344,098; 3,462,388; 3,467,642; 3,639,243; 4,070,296; 4,375,357; 4,568,624; 3,553,133; 3,852,208; 4,051,183; 4,194,877; 4,217,406; 4,339,237 and 4,397,651.
In addition, there are illustrated in U.S. Pat. No. 4,645,727, the disclosure of which is totally incorporated herein by reference, toner compositions comprised of resin particles with covalently bonded polymeric dye chromophores, which resins are of the formula as recited in claim 1. More specifically, this patent discloses and claims toner and developer resins containing covalently bonded dye chromophores of the following formula ##STR3## wherein A is selected from the group consisting of alkylene and arylene; B is selected from the group consisting of ##STR4## wherein R is an alkylene group, an arylene or polyether segment; D is selected from the group consisting of dioxyalkane or dioxyarene; x is a fraction number of from 0.01 to 0.50; and y is a fraction number of from 0.50 to 0.99, the sum of x+y being equal to 1. In contrast, there are selected for the colorants of the present invention polymeric dyes where, for example, there are absent any D-B segments. Also, with the toners of the present invention there can be selected lesser amounts of the polymeric dye while enabling a color intensity equal to or greater than the colored toners of the U.S. Pat. No. 4,645,727. There are also disclosed in this patent toner and developer compositions wherein the resins can be selected as colorants in conjunction with suitable resin hosts, reference the disclosure in column 12, lines 49 to 58. However, these resins are structurally complex, their syntheses complicated, and difficult to control. In addition, the terpolymeric nature and the high molecular weights of the color resins of the U.S. Pat. No. 4,645,727 could limit the number of the compatible host resins that may be utilized. In contrast, the polymeric dyes of the present invention, which are selected solely as colorants, are of a lower molecular weight; and they can be synthesized easily, and in relatively short time periods.
Although the above-described toner and developer compositions are suitable for their intended purposes, there continues to be a need for new compositions. Specifically, there is a need for colored toner compositions wherein dye aggregation and dye bleeding are eliminated. Also, there is a need for colored toner compositions which retain their color intensity for extended time periods. There is also a specific need for colored toner compositions wherein the colorants exhibit no tendency to leach, bleed, or sublime. Further, there remains a need for colored toner compositions wherein the colorants selected are uniformly dispersed thus imparting greater clarity and brightness to the resultant electrophotographic prints. Additionally, there is a need for toner compositions wherein the colorants selected permit high color quality and excellent color fidelity.